Glycine: Benefits, Side Effects, Best Time to Take It & More

Glycine

(L-Glycine)

Evidence: High
Possible Benefits: Reasonable
Safety: Very High

What is glycine?

Glycine is a non-essential amino acid. As a supplement, it is often used for reducing fatigue and improving sleep quality. This article is about the main benefits of glycine, its potential side effects, the best time to take it, and more.

What does glycine do for the body?

Since glycine is a non-essential amino acid, you do not need to consume it to survive. However, this amino acid still plays an important role in human health.

Glycine is a component of collagen, which is needed for proper joint health and other collagen-related effects. About 25% of collagen by weight is glycine. Unfortunately, supplemental glycine doesn’t seem to improve joint health.

This amino acid acts as a precursor to a variety of molecules, such as creatine.

Glycine can also act as a neurotransmitter. It can have both stimulating and sedative effects.

Possible benefits

All of the potential benefits mentioned below are dose-dependent. Generally, the higher the dose, the more pronounced the effects are. However, they do reach a plateau at a certain point. We will discuss the best dosing protocol later in this article.

Major benefits

Improved sleep quality – Multiple studies show that glycine supplements (about 3 grams taken an hour before bed) can increase sleep quality on the following night.
Reducing the negative effects of methionine – These two amino acids have to be kept in balance as too much of one (methionine, in particular) without enough of the other can cause unnecessary harm. For every gram of methionine, you need to consume at least half a gram of glycine if you wish to prevent side effects related to too much methionine. For optimal health, try to get about 1 gram of glycine for every gram of methionine.

Minor benefits

Improved cognition – This effect is secondary to improving sleep quality. In people who sleep well without the supplement and aren’t schizophrenics, glycine is unlikely to have a notable effect on cognition.
Reduced fatigue – This benefit is also secondary to improving sleep quality and doesn’t seem to apply to people who sleep just as well without supplemental glycine.
Reduced symptoms of schizophrenia – Glycine can reduce symptoms of schizophrenia when taken at extremely high doses (800+ mg/kg/d). This dose seems too impractical and may not be safe to take in the long term.
Improved insulin sensitivity – Low serum glycine levels are associated with insulin resistance. However, this is likely because insulin resistance leads to a depletion in glycine.

Possible side effects

These side effects are dose-dependent. The risk for them increases (often linearly but sometimes exponentially) as you increase the dose. Some of the side effects only apply to very high doses.

Amino acid imbalance – Essential and non-essential amino acids should be kept in balance as they act synergistically in many ways. Too much of one amino acid can sometimes cause side effects if there isn’t enough of another amino acid. For example, this principle applies to glycine and methionine, lysine and arginine, and the BCAA trio. There are many other proven and unproven examples. Food or a protein powder is usually a better choice for getting enough amino acids unless you have a specific goal in mind targeted by a particular amino acid/s.
Toxicity – While acute toxicity has never been reported, taking high amounts of glycine could lead to chronic toxicity and cause some health problems. To prevent chronic toxicity, it is best to stay below 6 grams a day unless you have a great reason to take more.
Contamination – Contaminated supplements are uncommon in the USA and other well-regulated countries. However, if you wish to buy products from China, India, or other countries without strict regulations, beware that the supplements may be contaminated. Either way, you need to choose the brand you order from wisely. It is highly recommended to check the certificates or read through some reviews for the specific product before you buy it. The FDA (Food and Drug Administration) has the power to regulate dietary supplements but can only do so after they have been on the market for a while. That’s because supplement companies are not obligated to announce to the FDA when releasing a new product on the market. The FDA has to discover the product and test it for potential impurities, which can take a lot of time. During that time, the supplement can be sold on the market even if it’s impure. Also, supplement companies can change their manufacturers without announcing it to the FDA.

Who should not take glycine?

You should probably avoid taking the supplement if you:

get enough glycine from food
experience a severe adverse reaction after taking the amino acid
are on a tight supplement budget (since there are more cost-effective supplements on the market for most people)

Who will benefit the most?

You should consider taking the supplement if you:

eat high amounts of methionine (for optimal health, you should get at least half a gram (preferably a full gram) of glycine for every gram of methionine)
have difficulty falling asleep
consume very little protein (less than 0.3 grams/pound of body weight)
suffer from insulin resistance
are pregnant (pregnant women need more glycine)

How much glycine should you take?

Since this amino acid can be found in food or synthesized in the body, you may already get sufficient amounts without taking it as a supplement. About 0.36 grams of protein/pound of body weight should generally be enough to prevent any symptom deficiency.

If you plan to take glycine as a supplement, 3-5 grams appears to be the best daily target for most people. This amount should provide most of the benefits without meaningful side effects.

Some people may benefit from doses higher than 5 grams. These include schizophrenics, carnivores with a high methionine intake, and people with difficulty sleeping.

Glycine can reduce symptoms of schizophrenia when taken at extremely high doses (800+ mg/kg/d). This dose seems too impractical and may not be safe to take in the long term.

Beware that for optimal health you should get at least half a gram (preferably a full gram) of glycine for every gram of methionine.

The upper safety limit for glycine is not well-established. To stay on the safe side, don’t take more than 6 grams daily unless you have a great reason to do so. Higher amounts may cause problems if you take the supplement for a prolonged period.

Food sources of glycine

An average diet provides about 2 grams of glycine.

Glycine is found in all whole foods that contain dietary protein.

The amount of glycine per gram of protein varies from food to food but a general rule of thumb is that the more protein you eat, the more glycine you are getting from food.

Beware that for optimal health you should get at least half a gram (preferably a full gram) of glycine for every gram of methionine.

This is generally the ratio people get from their diet. However, people who eat lots of muscle meat (the richest source of methionine) without getting enough glycine can throw this ratio off balance. This can cause long-term negative effects on their health.

The easiest way to find out exactly how much glycine, methionine, or other amino acids you are getting from food is with Cronometer.com. This free app allows you to track all vitamins, minerals, and more.

Best time to take glycine

Like most other amino acids, glycine is water-soluble, so you don’t have to take it with food to absorb it well. Taking the supplement with food is better if it causes stomach upset when you take it on an empty stomach.

To maximize the benefits, take glycine before falling asleep. One of the main benefits of the supplement is improving sleep quality.

If you practice time-restricted eating, take this amino acid during your eating window to guarantee it won’t break your fast.

Unless it feels too impractical, spread the daily dose into 2+ smaller doses throughout the day.

Interactions

Methionine
For every gram of methionine, you need to consume at least half a gram of glycine if you wish to prevent side effects related to too much methionine. For optimal health, try to get about 1 gram of glycine for every gram of methionine.
Other amino acids
Essential and non-essential amino acids should be kept in balance as they act synergistically in many ways. Too much of one amino acid can sometimes cause side effects if there isn’t enough of another amino acid. For example, this principle applies to glycine and methionine, lysine and arginine, and the BCAA trio. There are many other proven and unproven examples. Food or a protein powder is usually a better choice for getting enough amino acids unless you have a specific goal in mind targeted by a particular amino acid/s.
Vitamin B3
Vitamin B3 supplements (such as niacinamide, nicotinic acid, NR, and NMN) can deplete levels of TMG (trimethylglycine) in the body. If you’re taking nicotinic acid, combine it with half the dose of glycine to prevent liver toxicity. For example, for 1000 mg of nicotinic acid, take 500 mg of glycine. With the other forms of vitamin B3, you don’t need to worry about glycine as much.
Clozapine
Clozapine (Clozaril) is used to help treat schizophrenia. Glycine may decrease the effects of Clozapine and thus shouldn’t be taken with the drug.

Where to buy glycine

Amazon is the best option for ordering glycine supplements in most countries. They offer some very affordable products backed by many positive reviews. Also, you can choose from a wide range of brands without having to search through other markets on the internet.

Beware some brands display the dosage per serving instead of per pill or capsule. Therefore, you may accidentally buy something less potent than you intended. Do not fall for this marketing trick.

FAQ

You can take the amino acid daily and do not need to cycle it. However, it is certainly not a problem if you don’t take it daily. Not taking the supplement every once in a while could lead to better absorption. That is yet to be proven or disproven.

All of these options are fine. The two most important things to consider are the price and dosing. Powders are almost always the cheapest form. However, you may need a highly accurate scale to dose them correctly (preferably 0.001g). You can get one for as little as $20 from Amazon. Dosing the powders also takes some time that can add up over months or years. The disadvantage of capsules is that they often contain bovine gelatin, which rarely comes from an ethical source.

Yes. Most amino acids, including glycine, absorb and digest well if you take them before falling asleep. In addition, glycine is somewhat effective at improving sleep quality when taken at night.

This amino acid should not become harmful once it exceeds the expiration date but can lose potency over time.

Keep the supplement in a cold, dark, and dry place, and it should remain just as potent for many months or even years.

While toxicity is rare, too much glycine in the system can cause some health problems, often related to causing an imbalance in other amino acids. It is best to stay below 6 grams a day to prevent these side effects.

You may need more of this amino acid if you:
– eat very little protein (less than 0.3 grams/pound of body weight)
– eat high amounts of methionine (for optimal health, you should get at least half a gram (preferably a full gram) of glycine for every gram of methionine)
– are pregnant
– suffer from insulin resistance
– have difficulty falling asleep

The half-life of glycine in the body is anywhere from 25-250 minutes. This amino acid stays in your system for about a day you consume it.

If you take glycine before bed to improve sleep quality, you may notice the benefits right after you wake up the next day. In the long term, you need to take the supplement for about 2-4 weeks to begin noticing the benefits.

You can easily find vegan-friendly glycine pills and powders but always check the label to be sure. If you buy the amino acid in a capsulated form, beware that the capsules often contain animal-based gelatin. Instead, find a brand that puts its products into cellulose capsules.

Like most other amino acids, glycine is water-soluble, so you don’t have to take it with food to absorb it well.

Unfortunately, there is not enough scientific data to know for sure. Higher doses of glycine might break your fast and lower its benefits to some degree, especially if you are fasting to activate autophagy. If you practice time-restricted eating, take this amino acid during your eating window so it doesn’t break your fast.

References

Most of the information provided in this guide is supported by scientific research that can be found and verified in the PubMed medical library. We highly encourage you to use the library to verify anything said in this article. We excluded from consideration studies that are either confounded or have a high conflict of interest.

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